When functioning normally, the heart produces rhythmic contractions and is capable of pumping blood throughout the body. The heart has specialized conduction pathways in both the atria and the ventricles that enable excitation impulses (i.e. depolarizations) initiated from the sino-atrial (SA) node to be rapidly conducted throughout the myocardium. These specialized conduction pathways conduct the depolarizations from the SA node to the atrial myocardium, to the atrio-ventricular node, and to the ventricular myocardium to produce a coordinated contraction of both atria and both ventricles.
The conduction pathways synchronize the contractions of the muscle fibers of each chamber as well as the contraction of each atrium or ventricle with the opposite atrium or ventricle. Without the synchronization afforded by the normally functioning specialized conduction pathways, the heart's pumping efficiency is greatly diminished. Patients who exhibit pathology of these conduction pathways can suffer compromised cardiac output.
Cardiac rhythm management (CRM) devices have been developed that provide pacing stimulation to one or more heart chambers in an attempt to improve the rhythm and coordination of atrial and/or ventricular contractions. Cardiac rhythm management devices typically include circuitry to sense signals from the heart and a pulse generator for providing electrical stimulation to the heart. Leads extending into the patient's heart chamber and/or into veins of the heart and/or attached to the heart are coupled to electrodes that sense the heart's electrical signals and deliver stimulation to the heart in accordance with various therapies for treating cardiac arrhythmias and dysynchronies.
Pacemakers are CRM devices that deliver a series of low energy pace pulses timed to assist the heart in producing a contractile rhythm that maintains cardiac pumping efficiency. Pace pulses may be intermittent or continuous, depending on the needs of the patient. There exist a number of categories of pacemaker devices, with various modes for sensing and pacing one or more heart chambers.
A pace pulse must exceed a minimum energy value, or capture threshold, to “capture” the heart tissue by generating a propagating depolarization wave that results in a contraction of the heart chamber. It is desirable for a pace pulse to have sufficient energy to capture the heart chamber without expending energy significantly in excess of the capture threshold.
If the pace pulse energy is too low, the pace pulses may not reliably produce a contractile response in the heart chamber, resulting in ineffective pacing. If the pace pulse energy is too high, the pacing pulses produce capture, but may also inadvertently stimulate the heart in an undesirable mode or may undesirably stimulate other body structures. The present invention provides an approach for determining energy parameters for cardiac pacing and/or other therapeutic electrical stimulation that produces a desired activation, such as capture, and avoids undesirable activation.